...when the packets coming from your card arrive at your router or modem, your nic's mac will be replaced with the modem's/router's mac. And so on, the packets you sent travel through a bunch of gateways/routers and the source MAC address is always replaced with the previous device's mac address. The remote host you are communicating with will never know your mac.

So if you are trying to hide your identity over the internet, IP spoofing is VERY difficult (at least over TCP/IP on modern systems) and MAC spoofing is unnecessary.

If you ARE looking to hide yourself on a LAN rather than over the internet, then IP spoofing is pretty easy (provided you can easily sniff traffic to and from your victim) and MAC spoofing is a good idea.

The only reason why I only labelled the modem as your mac, is because that is the only mac that will be seen by the outside world in which case makes it visually easier to understand. The others do not then require labeling. But yes yours is also correct.